It is becoming increasingly desirable to provide onboard diagnostic means for certain components of an internal combustion engine, especially those which have a significant impact on critical engine performance criteria. This is particularly true in the motor vehicle industry, where high precision in the control of fuel flow has become essential to various present and planned engine management features designed to meet increasingly strict emissions, performance, drivability, and maintenance objectives. It is now well known how to adjust the fuel flow to the cylinders of an engine to maintain a desired fuel/air mixture ratio for meeting engine emission requirements by electronically controlling the actuation timing and duration of the engine's fuel injectors. Electronic fuel injector controls are presently available and in use, generally being incorporated into electronic engine control (EEC) modules performing a variety of engine control functions. In accordance with such known systems, the timing of injector actuation is controlled by the timing of the corresponding actuation signal sent by the control module. The duration of injector actuation, during which fuel is passed through the injector from a fuel rail or like fuel supply means, is controlled by the duration of the actuation signal from the control module, that is, by the pulse width of the signal.
Reliably controlling a fuel injector's fuel supply by controlling its actuation signal timing and pulse width requires that the fuel injector be performing properly. A fuel injector's performance may deteriorate, however, over a period of use, potentially resulting in decreased engine efficiency, increased emission of undesirable combustion products, etc. A defective injector spring or a malfunctioning electromagnetic solenoid in the injector, for example, may change the response of the injector to a given actuation signal, specifically, the timing of the injector opening and/or closing events. Thus, in support of maintaining the efficacy of electronic engine management devices adapted to control fuel flow by controlling the actuation of fuel injectors, it would be desirable to provide means for detecting malfunctioning fuel injectors. It is an object of the present invention to provide such means for detecting malfunctioning injectors and, in particular, it is an object of the invention to provide an on-board diagnostic system to periodically test an engine's fuel injectors during engine operation without requiring disassembly of the engine. Additional objects and features of various embodiments of the invention will be apparent from the following disclosure.